1. Field
The present invention relates to an optical device. For example, the optical device relates to an optical switch that which is suitable for a wavelength division multiplexing (WDM) transmission system.
2. Description of the Related Art
Recently, in order to process rapidly increasing amounts of traffic data on the Internet, optical networks and optical interfacing using the wavelength division multiplexing (WDM) as their nucleus are being constructed at a high pace. The current network (WD transmission system) configuration has been developed from the point-to-point type network configuration in which two base stations (transmission terminal station devices) are directly connected, into the ring type or mesh type network configuration.
Hitherto, the channel switching, multiplexing (ADD), or demultiplexing (DROP) of optical signals in an optical transmission device has been performed by the electrical switching with respect to electric signals that have been converted from optical signals. However, the optical switch using the wavelength selective switch (WSS) for directly switching optical signals allows switching without converting optical signals into electric signals, to thereby enable an increase in the switching speed, and dynamic setting or change of routes. With this being the case, the provision of the WSS to the channel switching or the like has been studied in recent years.
The optical switch using the WSS plays a role also in reducing the module mounting area in a unit or the cost reduction. Such an optical switch can individually changes routes of single-wavelength light beams included in inputted wavelength multiplexed signal light, and again wavelength-multiplex the changed n-single wavelength light beams and output them as required. Here, the wavelength of each single-wavelength light beam is prescribed by specifications referred to as IUT grid, standardized by the ITU (International Telecommunication Union), so as to conform to this IUT grid.
Regarding the constructions of conventional WSSs, because many of them use diffraction gratings, they need to earn dispersion in order to obtain a desired property, leading to an increase in an optical path length. This results in an increased module size. In order to downsize the WSS, therefore, spectroscopic elements with a large dispersion become indispensable. One method for increasing dispersion is to apply optical waveguides to the spectroscopic elements. Use of the optical waveguide allows an optical path difference to be made by the core pattern of the optical waveguide, thereby enabling a diffraction order to be freely selectable. For example, in arrayed waveguide gratings (AWG) constituting a typical optical waveguide type demultiplexing device, ones having diffraction orders ranging from about 12 to about 74 have been realized (refer to the following patent document 1). Because the dispersion of the AWG is proportional to the diffraction order, a large diffraction order allows spectroscopic elements with large dispersion to be realized, thereby enabling size-reduction.
Related techniques are discussed in the following documents. The Japanese Laid-open Patent Publication No. 2005-283932 describes wavelength selective switches using MEMS mirrors, and the Japanese Laid-open Patent Publication No. 2004-117449 and Japanese Patent No. 2986031 each describe a waveguide type wavelength selective switch. Japanese Laid-open Patent Publication No. 2003-185866 sets forth a construction example in which a photodiode is mounted on a waveguide.
Because the WSS is an optical device functioning in accordance with a signal wavelength, it is desired that the signal interval is a constant wavelength interval. However, the ITU prescribes that the signal light interval is a frequency interval 100 GHz (or 50 GHz), and therefore, when this frequency interval is converted into a wavelength interval, the interval does not become constant, and focus images of light beams for each channel, demultiplexed by the demultiplexing elements serving as the WSSs become unequally spaced. In this case, if optical routes for each channel are switched using equally spaced MEMS mirrors, reflecting surfaces (focus images) with respect to the mirrors differ with each other, so that there occurs a problem of causing deterioration of pass bands, or leading to an occurrence of variations in the pass bands for each wavelength.
A possible method for inhibiting such an occurrence of variations in pass bands is one in which the unequal wavelength interval is converted into an equal interval by exercising one's ingenuity to the construction of the MEMS mirror or the like, or by using a wedge-shaped prism. However, in the former case, since it is necessary to design the MEMS mirrors to be unequally spaced so as to become optimal with respect to each wavelength, the difficulty level of the design is increased, so that the MEMS mirrors become specialty items. This leaves room for improvement in general versatility. In the latter case, since the prism is additionally arranged as a new optical member, insertion loss increases, and in addition, a workload for the adjustment of the alignment of an optical system, or the difficulty level of assembly increases, which can result in an increased number of man-hours for work.
Suzuki, “Allayed Waveguide Diffraction Grating (AWG) Device”, the Journal of the Institute of Electronics, Information and Communication Engineers, Vol. 82, No. 7, pp. 746 to 752 (1999) discusses a technique for solving the above-described problems.
The WSS is expected to be used for a node having an OADM (optical add drop multiplexer) function and an OCX (optical cross-connect) function in a ring-type or mesh-type construction that is supposed to become the next generation of network configuration. In this case, for a function of an optical device installed on the node described above, it is expected to allow, not only information on the light power, but also information on the wavelength number and the wavelength allocation to be obtained as monitor information on signal light, regarding light outputted from each port.
In order to monitor light outputted from each port, a construction is supposed that takes out a part of light outputted from the port by branching it with a tap coupler or the like, and that monitors the light power, the wavelength allocation or the like for each wavelength component, using a simplified spectrum analyzer. However, there arises a need to form a module for an optical monitor at the outside of the port, separated from the construction as the wavelength selective switch. Especially when using monitoring results for the control of mirror angles of the MEMS mirrors, communications between modules must be performed, so that a circuit construction such as ICs for communication is supposed to have to be separately provided. This leaves room for improvement in reducing the apparatus scale.
Another possible construction stores in advance information on the attenuation amounts of output light with respect to the angle variation amounts of light reflecting elements such as the MEMS mirrors, and performs optical level corrections (adjustments) through the control of reflecting surface angles of the MEMS mirrors, to thereby realize VOA function control. Specifically, this construction records information on the angle variation amounts of the MEMS mirrors, and correction information on the temperature characteristics of the angle variation amounts, in a memory of a digital signal processor (DSP) or the like, to thereby move the MEMS mirrors by the angle recorded in accordance with a set attenuation amount. However, the angle control for the MEMS mirrors is not easy to perform at a high degree of accuracy, and in addition, it has a possibility of deteriorating over time, thereby raising concerns for long-term reliability. Therefore, regarding the angles of the MEMS mirrors, the function of performing feedback control in response to light amounts is an important matter under the current circumstances.
In the patent document 1, regarding the wavelength selective switch, a construction is disclosed wherein a plurality of single-wavelength light beams that are switched in routes for each wavelength are multiplexed to thereby output them as second wavelength multiplexed light, and wherein a part of the second wavelength multiplexed light is branched, as well as the branched light is demultiplexed for each wavelength component, and physical amounts of respective demultiplexed light beams are monitored. However, since this construction adopts a redundant arrangement so as to again demultiplex the second wavelength multiplexed light, it hinders the reduction in insertion loss, the cutback of the number of components, and the decrease in mounting area.
Accordingly, the present invention is characterized by the following mirror unit and optical switch.
(1) That is, the mirror unit according to the present invention is characterized by comprising a mirror device in which a plurality of movable mirrors are provided at equal intervals; and interfaces that perform optical axis corrections such that each reflection target light beam to be made to be reflected on a respective one of the plurality of movable mirrors has an optical axis corresponding to the installation position of the respective one of the movable mirrors, whereupon the interfaces introduce each of the reflection target light beams into the respective one of the movable mirror.
(2) The optical switch according to the present invention is a switch including a plurality of optical ports into/from which light beams are inputted/outputted, and switching the light beams outputted through the optical ports in wavelength units, characterized by comprising spectroscopic elements that spectrally separate light beams inputted from the optical ports and outputs them as light beams with optical axes different for each wavelength; a mirror device in which a plurality of movable mirrors are arranged at equal intervals, which causes respective light beams for each wavelength outputted from the spectroscopic elements to reflect, and which allows the optical ports of output destinations to be switched by making the angles of the reflecting surfaces variable; and a plurality of mirror interfaces each provided on the optical paths between the movable mirrors and the plurality of optical ports mediated by the spectroscopic elements, wherein light beams that have been spectrally separated by the spectroscopic elements and that have optical axes different for each wavelength are inputted into the mirror interfaces, and the mirror interfaces subject the light beams to an optical axis corrections such that each of the input light beams has an optical axis corresponding to the installation position of the movable mirror for causing one of the respective one of the wavelength lights to reflect, whereupon the mirror interfaces introduce each of the input light beam into the respective one of the movable mirror.
(3) Furthermore, in the above (2), each of the mirror interfaces may include a substrate; and a plurality of correction waveguides that is formed on the substrate, that have reflection target light beams inputted from one end face of the substrate, and that perform optical axis corrections such that the inputted reflection target light beams have optical axes corresponding to the installation positions of the respective plurality of movable mirrors, wherein the light beams that have propagated through the optical axis correction waveguides may be emitted from the other end face of the substrate to the respective movable mirrors.
(4) Moreover, in the above (2), the spectroscopic elements are a plurality of arrayed waveguide devices provided in correspondence with the respective plurality of optical ports, and each of the arrayed waveguide devices may include a substrate; and an AWG (arrayed waveguide gratings) waveguide that has a plurality of output waveguides formed on the substrate through which the spectrally separated light beams by wavelength each propagate, wherein the plurality of mirror interfaces may be integrally formed with the plurality of arrayed waveguide grating devices provided in correspondence with the respective plurality of optical ports, and wherein each of the mirror interfaces may include the substrate constituting the corresponding arrayed waveguide grating devices; and a plurality of correction waveguides that are formed on the substrate, that are connected to the respective plurality of output waveguides constituting the AWG waveguides, and that perform interval corrections such as to cause the intervals of the plurality of output waveguides to correspond to the installation intervals of the plurality of movable mirrors.
Furthermore, in the above (3) or (4), a light receiving element that monitors light propagating through a corresponding correction waveguide may be mounted on the installation position of each of the plurality of correction waveguides in the mirror interface, and in addition, a control unit for controlling the reflecting surface angles in the movable mirrors in response to monitoring results in the light receiving element may be provided.